HJ30x series devices monitor current consumption to ensure that pre-set current levels are not exceeded. They measure current in all three phases and shed load if the current exceeds the pre-set limit.

These devices find application with electric underfloor heating systems where there is a supply with a restricted capacity. The current range setting is set via DIP switch with increments of 1A up to a maximum of 100A. They are easily installed within a consumer unit where they occupy 6 module widths.

The highly accurate microprocessor-based design uses Discrete Fourier Transformation (DFT) to calculate effective current values to eliminate effects of temporary short circuits and transient current during motor start up.

The HJ303 (order code 2457) has 1 output per phase and the HJ306 (order code 2458) has 2 outputs per phase. If the pre-set current is exceeded in any phase, the first load is disconnected. If the pre-set current is exceeded again a second load will be disconnected after 3 seconds.